Vehicles used in polluted atmospheres, such as those used in mining or agricultural work, are equipped with air filtration equipment for protecting the operators of such equipment from airborne contaminants. Such vehicles typically have an enclosed operator cab and a ventilation system having an air inflow conduit for feeding a motor-driven fan or blower. The fan induces air to flow through a dust filter and in some installations, an activated-charcoal filter for adsorbing harmful vapors/gases, after which the filtered air is conveyed into the operator cab.
Enclosed operator cabs can provide very high levels of protection from airborne contaminants so long as clean, filtered air is introduced into the cab with positive air pressurization of the cab interior. However, leaks in the ventilation system can allow airborne contaminants to enter the operator cab. Typically, the areas within a ventilation system that have a tendency to cause leaks include the sealing area around the filter, the joints between separate portions of ductwork, and the openings in the ductwork provided for the electrical wiring of the fans. If major leaks occur, the effectiveness of the cab filtration system can be severely diminished, thereby compromising the safety of the operator. Thus, the ventilation system should be periodically leak tested to ensure the cab enclosure provides sufficient protection for the operator.
One method for leak testing the ventilation system of a cab enclosure is specified in ASAE (American Society of Agricultural Engineers) Standard S525. In this method, the vehicle being tested is driven over a non-paved surface to increase the levels of aerosol and dust in the atmosphere surrounding the vehicle. As the vehicle is driven, one optical particle counter is used to measure ambient aerosol and dust concentrations outside the operator cab of the vehicle and another optical particle counter is used to measure aerosol and dust concentrations inside the operator cab. For a cab to be considered acceptable, the ratio of the concentrations outside the cab to the concentrations inside the cab must be greater than 50. Heitbrink et al., “Review of Ambient Aerosol Test Procedures in ASAE Standard S525,” Journal of Agricultural Safety and Health, 4(4): 255-266 (1998).
The foregoing method suffers from the drawback that the concentration of ambient aerosols varies with location and time of year. Thus, the test can be impractical in certain locations or during certain times of the year when the ambient aerosol concentration is not large enough to overcome any extraneous aerosol generation in the cab. Id.
In another method for leak testing the ventilation system of an operator cab, the cab is placed inside a laboratory test chamber and exposed to an atmosphere containing a constant level of ethyl acetate. During the test, the ventilation system of the cab is operated to cause the surrounding atmosphere to flow through a filter capable of filtering ethyl acetate and into the interior of the cab. A gas monitor placed inside the cab is used to detect for the presence of leaks in the ventilation system by monitoring the concentration of ethyl acetate inside the cab. Although more reliable than the method for testing cabs in the field set forth by ASAE Standard S525, laboratory testing is much more inconvenient than such field-testing since the cab to be tested must be driven or otherwise transported to a testing facility.
Accordingly, there exists a need for new and improved systems for leak testing ventilation systems of enclosed operator cabs.